Interferometers have been used to investigate fundamental physical principles such as to determine the existence of gravitational waves and to disprove the existence of an electromagnetic ether. Due to the many applications of interferometers, the improvement of interferometers remains an active area of research. In many cases, interferometers divide an input beam into two portions, one of which is then subject to a phase change associated with a parameter under investigation. The two portions are then recombined, and the resulting interference detected. Phase change detection sensitivity is generally related to beam power (i.e., number of photons) and the quantum state. Coherent states are typically associated with phase uncertainties that are proportional to √{square root over (N)}, wherein N is a number of photons used. Such phase uncertainties correspond to the shot noise limit. Further improvements in detection sensitivity can be made using so-called squeezed light.
Another approach to reducing phase uncertainty is to increase the magnitude of a detected interference signal using a nonlinear interferometer (NLI). In such an interferometer, passive beam splitters are replaced by nonlinear optical parametric amplifiers. Unfortunately, conventional nonlinear interferometers have been implemented as Mach-Zehnder interferometers, typically requiring active stabilization, and improved NLI configurations are needed.